As the computer technologies for a hardware and software have significantly been advanced, most of portable data terminals have a performance and mobility improved. The portable data terminals are now widely used by a mobile business person, and used for novel application proposed day by day.
The portable data terminal is hence required to reduce their overall dimensions and weight and particularly improve and enhance a power-saving function, i.e., a less energy consumption. Saving the power consumption contributes reducing a battery size, thus reducing both an overall size and a weight of the portable data terminal.
The power saving function may be interpreted by developing a standby state where a power in consumed as little as possible, hence being traded off with a utility. Pursuing the power saving too much makes an activated state and the standby state be switched frequently and creates some drawbacks such as a delay of a response and an intricate operation shifting from the standby state to the action state. The power saving hence requires to determine shifting conditions and power saving levels.
Shifting to the power saving operation mode may be implemented by a power switch of the data terminal operated by a user or by monitoring a non-operation period more than a specified one.
As Japanese Patent Laid-open No.10-133788 discloses, upon being informed that a portable data terminal is turned off, a host computer turns off the computer itself and then shut down an entire system, thus exhibiting a most power saving effect.
Above prior art allows the shifting to the power saving operation mode automatically conducted without any troublesome operation. Both the portable data terminal and the computer are completely turned off and thus reduce the power consumption. However, the user needs to shift the power saving operation mode back to the ordinary operation mode with a user's deliberate operation.